This invention relates to microwave space fed phased array antennas and, in particular, to a three-dimensional cylindrical microwave lens antenna for wideband scanning applications.
Microwave space fed antenna arrays which are capable of directively radiating wideband radio signals and steering their beams over a wide range of angles in both azimuth and elevation are widely utilized in tactical and strategic radar and surveillance systems, wideband microwave communication systems, radio aids for navigation and as electronic counter-measures antennas.
Conventional phased array antennas radiate a single directive beam which is steered by means of phase shifters located at each radiating element. However, the bandwidth of these arrays is limited since phase shifters are not true time delay units, which would be required for proper bandwidth compensation of path length differences encountered during beam scanning.
Current methods for overcoming this bandwidth limitation involve sub-arraying or dividing the aperture into sub units. This requires a limited number of time delay units combined with a large number of phase shifters at the radiating element level. This approach has not been wholly satisfactory, however, since the time delay units are complex and contribute to high insertion losses and high side lobes in the antenna.
Other state-of-the-art systems that require wide angle scan in both azimuth and elevation with wideband performance often use stacks of bootlace lenses feeding an orthogonal set of similar lenses. Unfortunately, for moderate to high gain antennas this arrangement can be very bulky, expensive, complex, unreliable and heavy.
Accordingly, there currently exists the need for a space fed phased antenna array which can scan a directive beam in azimuth and elevation without using complex time delay units at each radiating element and without the usual bandwidth restrictions in phased arrays caused by path length differences during scan. The present invention is directed toward satisfying that need.